Enhanced detection sensitivity of neuronal activity patterns using CaMPARI1 vs. CaMPARI2

Area of Science:

• Neuroscience
• Molecular Biology
• Genetics

Background:

• Calcium-modulated photoactivatable ratiometric integrators (CaMPARI) are genetically encoded fluorescent sensors used to track neuronal activity.
• CaMPARI enables irreversible photoconversion, capturing snapshots of neural activity for mapping synaptic connectivity and recording large-scale activity in freely moving subjects.
• CaMPARI2 was developed to improve contrast and reduce Ca2+-independent photoconversion compared to CaMPARI1.

Purpose of the Study:

• To compare the performance of CaMPARI1 and CaMPARI2 in vivo.
• To evaluate the efficiency and sensitivity of CaMPARI sensors in capturing neuronal activity.
• To assess the effectiveness of in vitro screening methods for CaMPARI optimization.

Main Methods:

• Side-by-side comparison of CaMPARI1 and CaMPARI2 in mouse cortex and hippocampus.
• Evaluation of photoconversion efficiency and red-to-green fluorescence ratio in active neurons.
• Assessment of Ca2+ sensing capabilities and dynamic fluorescence changes.

Main Results:

• CaMPARI1 showed a higher red-to-green ratio in active cells compared to CaMPARI2.
• CaMPARI1 exhibited greater sensitivity as a Ca2+ sensor, producing larger activity-driven fluorescence changes.
• Optimization of CaMPARI2 led to reduced photoconversion efficiency in active neurons.

Conclusions:

• CaMPARI1 outperforms CaMPARI2 in terms of photoconversion efficiency and Ca2+ sensitivity in vivo.
• In vitro screening assays did not accurately predict the in vivo performance of CaMPARI2.
• Future CaMPARI optimization should incorporate in vivo screening and validation to improve predictability.